Bangladesh J. Bot. 39(2): 179-183, 2010 (December) COMPARATIVE MORPHOLOGY AND FLORAL BIOLOGY OF THREE SPECIES OF THE GENUS NYMPHAEA FROM BANGLADESH * 1 HOSNE ARA BEGUM KK GHOSAL AND TK CHATTOPADHYAY Department of Genetics and Plant Breeding, Bidhan Chandra Krishi Viswa Vidyalaya (BCKVV), West Bengal, India Key words: Nymphaea, Comparative morphology, Floral biology Abstract Morphology and floral biology of three species of the genus Nymphaea (Nymphaeaceae) of Bangladesh revealed that N. nouchali, N. pubescens and N. rubra, were normal, protogynous or normal and protogynous, respectively. N. pubescens was night bloomer and each flower opened for three consecutive nights where as N. rubra opened for four consecutive nights and N. nouchali for three consecutive days. The behavior of anther dehiscence and stigma appendages had significant role in pollination. Excellent pollen germination and receptivity were observed in the exudate of stigma cup. Introduction As Nymphaea pubescens Willd. (Nymphaeaceae) is the national flower of Bangladesh, Its improvement with respect to economic and aesthetic aspect is of great significance. Prior to the genetic improvement of Nymphaea, study on morphology and floral biology in Bangladeshi materials were demanding. Other species should also be considered to study morphological variations. Three local species, namely N. nouchali Burm. f., N. pubescens Willd. and N. rubra Roxb. ex Andrews were studied in the present treatise. Floral biology studied by Schneider (1982), Prance and Anderson (1976) and Meeuse and Schneider (1980) on different species of Nymphaea mainly focused on protogynous nature and pollination mechanism. The present work is intended to study other behaviour of flowers that might influence the breeding behaviour of the species. Materials and Methods N. nouchali Burm. f., N. pubescens Willd., and N. rubra Roxb. ex Andrews collected from Bangladesh were studied. The results on floral biology were verified under tumbler condition both in Bangladesh and India. Morphological data of the species were taken from natural habitat of Bangladesh. Flowering and anthesis were recorded in September for three consecutive years. The opening and closing behaviour of flowers were measured with the help of a device developed by the author. The male reproductive nature was studied in respect of opening and closing of anthers, time of anther dehiscence and bending of stamens. The female reproductive nature includes protogyny, stigma appendages, stigma exudates and stigma receptivity. The protogynous nature was tested by comparing the time of anthesis, stigma receptivity and anther dehiscence. Observations on the behaviour of stigma appendages were recorded from flowers on their first, second and third opening. The time and duration of stigma exudate secretion were examined. The presence of stigma exudates on stigmatic cup or its moist condition was considered as indication of stigma receptivity. It was confirmed by in vivo pollen germination percentage. * Corresponding author. Department of Botany, Jagannath University, Dhaka, Bangladesh <[email protected]>. 1Department of Horticulture, BCKVV, West Bengla, India. 180 BEGUM et al. Results and Discussion Distinct morphological variations were observed in the N. nouchali Burm. f., N. pubescens Willd. and N. rubra Roxb. (Table 1, Fig. 1a-f). Nymphaea nouchali: Stem, erect and tuberous, leaves glossy on both surfaces, light-green above, with or without purple patch and reddish-violet to bluish-violet beneath, peltate, margin waved and slightly dentate, lobes rounded. Flowers small, light-blue. Sepals not ribbed, glossy, entire, acute, reddish-green with blue inner surface. Petals acute, light-blue. Stamens with blue sterile appendages at the tip. Anthers triangular in cross section. Anther and stigma yellow, stigma saucer shaped with horn like appendages. Excellent fruit-set, seeds ellipsoid, enclosed by aril, floating. Nymphaea pubescens: Stem, tuberous, erect, leaves ovate-elliptic, dentate, dark-green, glabrous above and purplish-green, pubescent and prominently veined beneath. Petioles and pedicels long. Sepals green and ribbed outside, white inside; Petals pure white, linear- oblanceolate and obtuse. Gradual transformation of petals towards stamen was prominent. Stamens arranged in three to four whorls, tip blunt and no sterile appendage. Anthers yellow, flat and possessed cream colored pollen grains. Anthers two-lobed, opened by longitudinal slit, introrse. Carpels many and syncarpous; stigmatic rays correspond to the number of carpels. Stigma cup shaped; stigma appendages oblong and yellow. Natural fruit formation observed which developed under water. Seeds ellipsoid, enclosed by transparent fleshy aril and floated on the water. Nymphaea rubra: Stem, tuberous, erect, leaves glabrous, reddish-green above and reddish, pubescent and veined beneath. Flowers crimson-red, becoming lighter during winter season and bloomed round the year. Sepals 4, ovate-lanceolate, obtuse, reddish-green, ribbed outside and crimson-red inside. Petals crimson-red. Anthers and stigma appendages deep crimson-red. Stigma appendages very long, densely arranged, covering the stigma completely. No fruit formed naturally. N. rubra resembled N. pubescens in other respects. The flower morphology of three Nymphaea species (Fig. 1a,b,c) in the present investigation is more or less similar to the observations of Mitra (1993) and Hossain et al. (2001). But it differed slightly with Conard (1905), Roxburgh (1932), Duthie (1960), Mosely (1961), Sen (1962), Prain (1963) and Khan and Halim (1979, 1987). Table 1. Comparison of flower morphology of Nymphaea species. Flower Number of Number of Length of Ovary Number of Length of Taxa diameter petals stamens sterile diameter ovary stigma appen- (cm) appendages (cm) chambers dages (cm) N. nouchali 8.60 ± 0.11 16.80 ± 0.6 75.50 ± 2.38 0.34 ± 0.12 2.10 ± 0.12 13.55 ± 0.45 0.19 ± 0.02 N. pubescens 11.35 ± 0.42 19.50 ±1.80 61.50 ± 0.80 Nil 1.47 ± 0.06 17.00 ± 0.32 0.51 ± 0.03 N. rubra 19.95 ±1.12 22.18 ± 0.67 82.90 ± 2.22 Nil 1.77 ± 0.11 22.40 ± 0.59 1.11 ± 0.07 The taxonomic rank of Nymphaea species varied between species and varieties in many of the cases. The work of Hossain et al. (2001) and Hassan (2009) confirmed the identify of the Bangladeshi species worked on by the authors. Flowering in N. rubra occurs round the year, while in the other two species flowering takes place from May to November. Optimum temperature for growth and flowering ranged from 31 to 36º C. Anthesis showed great variation among different species of Nymphaea. N. pubescens showed anthesis for three consecutive nights, N. rubra for four consecutive nights and in N. nouchali it COMPARATIVE MORPHOLOGY AND FLORAL BIOLOGY OF NYMPHAEA 181 was for three consecutive days. In all the species anthesis for the second time was found to take place about half an hour earlier. Opening and closing time of flowers were very much influenced by the intensity of sunlight and hence temperature also. According to Prance and Anderson (1976) temperature was more effective than sunlight for the opening and closing of Nymphaea flowers. The anthers were introrse and split longitudinally in all the species. In N. nouchali the anther lobes opened for ever but in N. rubra and N. pubescens opening and closing correspond to the spreading of petals. Fig. 1a-f. Top view of flowers showing stigma appendages: N. pubescens (a), N. rubra (b) and N. nouchali (c). Details of floral parts in longitudinal sections: N. pubescens (d), N. rubra (e) and N. nouchali (f). The time of anther dehiscence differed in the three Nymphaea species. In N. nouchali anthers burst 24 hours prior to the anthesis. N. pubescens showed dehiscence 24 hours before or after anthesis and in N. rubra it was during the second anthesis. In N. nouchali the anther of different whorls burst gradually from outermost to innermost whorl during successive anthesis. But in N. pubescens and N. rubra all the anthers burst simultaneously. At the second anthesis, the stamen tip gradually bent inwards in N. pubescens and N. rubra. The bending formed a cone and completely covered the stigma in N. rubra but in N. pubescens the loose cone leaves a terminal small opening. The case was reverse in N. nouchali where the non-dehiscent inner whorl bent inside and the dehisced anthers spread outside. Stigma showing receptivity before the dehiscence of anther indicated the protogynous nature of flowersd. N. rubra showed protogyny but N. pubescens was either protogynous or normal. N. nouchali was always normal. The results showed similarity with those of Schneider (1982), and Prance and Anderson (1976). Stigma appendages remain erect in first anthesis but bent from the 182 BEGUM et al. second anthesis. In N. rubra long stigma appendages completely covered the stigma inhibiting pollination. In N. pubescens the covering was partial and loose. Horn like small stigma appendages could not cover the stigma in N. nouchali (Fig. 1a,b,c). This behavior of the stigma appendages played an important role in breeding behaviour of the species. The flowers of all species showed their stigma cup full of stigma exudates in the first anthesis. In the second anthesis the stigma of N. rubra dried up but in N. nouchali and N. pubescens stigma cup remained sufficiently moist. Prance and Anderson (1976) observed fluid on the stigma cup of N. ampla in unopened bud condition but supposed it as lake water. Meeuse and Schneider (1980) found the sugar level of stigmatic exudate to be 1 - 1.5%, boron concentration 5 ppm and ionic composition in terms of Ca, K and Mg very close to optimal for pollen germination. The presence and role of exudate were observed by others (Heslop-Harrison and Shivanna 1977, Mosely 1961, Schneider 1982). The receptivity of stigma was confirmed by in vivo pollen germination. Pollen grain showed the highest germination percentage on the stigma of flowers opened for the first time. On second anthesis N. rubra lost its receptivity but N.